Zoom lens and camera with zoom lens

Abstract

A zoom lens of variable power ratio of the order of 3 in which the whole of the zoom lens is made up of three lens elements groups and the power configuration of each of the groups has an arrangement of negative, positive, and negative. The zoom lens includes, sequentially from an object side thereof, a first lens elements group which has a negative refraction power as a whole, a second lens elements group which has a positive refraction power as a whole, and a third lens element group, which has a negative refraction power as a whole. A variable power is realized by shifting the positions of the first and second lens elements group in the direction of an optical axis thereof.

1. A zoom lens comprising, sequentially from an object side thereof, a first lens elements group having a negative refraction power as a whole, a second lens elements group having a positive refraction power as a whole, and a third lens element group having a negative refraction power as a whole, wherein a variable power is realized by shifting positions of the first lens elements group and the second lens elements group in a direction of an optical axis thereof, or by shifting, in addition to the positions of the first lens elements group and the second lens elements group, a position of the third lens element group in a direction of an optical axis thereof,
 wherein the first lens elements group is made up by disposing, sequentially from an object side thereof, a first lens element which is a negative lens, which has a negative refraction power, a second lens element which is a positive lens, which has a positive refraction power, and a third lens element which is a negative lens, and 
 wherein the zoom lens satisfies the following conditional expression (1) with respect to a power of the first lens elements group, the following conditional expression (2) with respect to a size of the whole lens system, and the following conditional expression (3) with respect to a power of the third lens element group, the following conditional expression (4) with respect to a power of the second lens element, the following conditional expression (5) with respect to dispersion properties that are distributed to each lens element of the first lens elements group, and the following conditional expression (6) with respect to a refractive index of the second lens element:
   −0.8≦ f   w   /f   I ≦−0.45  (1) 
   4.5≦ TL   w   /f   w ≦7.5  (2) 
   −0.55≦ f   w   /f   III ≦0  (3) 
   0.22≦ f   w   /f   2 ≦0.55  (4) 
   15≦(υ 1 +υ 3 )/2−υ 2   (5) 
   1.65≦n 2   (6) 
 
 
     where:
 f w : composite focal length of the whole lens system at a wide-angle end; 
 f I : composite focal length of the first lens elements group; 
 f III : composite focal length of the third lens element group; 
 TL w : distance from an object side surface of the first lens element, which is positioned closest to the object side among lens elements of the first lens elements group, to an image plane at the wide-angle end (where, a parallel plane glass portion is converted into an air space distance); 
 f 2 : focal length of the second lens element of the first lens elements group; 
 υ 1 : Abbe number of the first lens element of the first lens elements group; 
 υ 2 : Abbe number of the second lens element of the first lens elements group; 
 υ 3 : Abbe number of the third lens element of the first lens elements group; 
 n 2 : refractive index relative to the d line of the second lens element of the first lens elements group. 
 
   
   
     2. The zoom lens according to  claim 1 , wherein the first lens element of the first lens elements group is an aspherical lens, and wherein the zoom lens satisfies the following conditional expression (7) with respect to a configuration of an image side surface thereof and also satisfies the following conditional expression (8) with respect to a relative characteristic on configuration between the object side surface of the first lens element and an object side surface of the second lens element of the first lens elements group:
   0.4≦ f   w   /r   2 ≦1.4  (7) 
   0.1≦ r   2   /r   3 ≦1.5  (8) 
 
     where:
 r 2 : radius of curvature of the image side surface of the first lens element of the first lens elements group; and 
 r 3 : radius of curvature of the object side surface of the second lens element of the first lens elements group. 
 
   
   
     3. The zoom lens according to  claim 1 , wherein the second lens elements group is made up by disposing, sequentially from an object side thereof, a fourth lens element which is a positive lens, a fifth lens element which is a positive lens, a sixth lens element which is a negative lens, and a seventh lens element which is a positive lens, and
 wherein the zoom lens satisfies the following conditional expression (9) with respect to a positive composite power of the fourth lens element and the fifth lens element, the following conditional expression (10) with respect to a negative power of the sixth lens element, the following conditional expression (11) with respect to dispersion properties that are distributed to the fourth lens element, the fifth lens element, and the sixth lens element, which are disposed closer to the object side in the second lens elements group, and the following conditional expression (12) with respect to a refractive index of each of the similar lens elements:
   0.5≦ f   w   /f   4,5 ≦1.5  (9) 
   −1.5≦ f   w   /f   6 ≦0.25  (10) 
   28≦(υ 4 +υ 5 )/2−υ 6   (11) 
   ( n   4   +n   5 )/2− n   6 ≦−0.24  (12) 
 
 
     where:
 f 4,5 : composite focal length of the fourth lens element and the fifth lens element of the second lens elements group; 
 f 6 : focal length of the sixth lens element of the second lens elements group (where, in the event that the sixth lens element makes up a composite aspherical lens, a composite focal length of a base spherical lens and a resin portion); 
 υ 4 : Abbe number of the fourth lens element of the second lens elements group; 
 υ 5 : Abbe number of the fifth lens element of the second lens elements group; 
 υ 6 : Abbe number of the sixth lens element of the second lens elements group (where, Abbe number of a glass material of a base spherical lens, in the event that the sixth lens element makes up a composite aspherical lens); 
 n 4 : refractive index relative to the d line of the fourth lens element of the second lens elements group; 
 n 5 : refractive index relative to the d line of the fifth lens element of the second lens elements group; and 
 n 6 : refractive index relative to the d line of the sixth lens element of the second lens elements group. 
 
   
   
     4. The zoom lens according to  claim 3 , wherein of refracting surfaces of each lens element of the second lens elements group, at least one of the refracting surfaces is formed into an aspherical shape, and wherein the zoom lens satisfies the following conditional expression (13) with respect to a configuration of an object side surface of the fourth lens element and the following conditional expression (14) with respect to an image side surface of the sixth lens element:
   0.2 ≦f   w   /r   7 ≦1.0  (13) 
   0.4 ≦f   w   /r   12 ≦1.6  (14) 
 
     where:
 r 7 : radius of curvature of the object side surface of the fourth lens element of the second lens elements group; and 
 r 12 : radius of curvature of the image side surface of the sixth lens element of the second lens elements group (where, radius of curvature of a boundary plane between resin and air in the event that the image side surface of the sixth lens element is made up of a resin lens surface of a compound lens). 
 
   
   
     5. A camera which installs thereon the zoom lens according to  claim 3 . 
   
   
     6. The zoom lens according to  claim 1 , wherein the third lens element group is made up of only a lens element which is a negative lens, and wherein the zoom lens satisfies the following conditional expression (15) with respect to a configuration of the object side surface of the lens element of the third lens element group:
   2.0 f   w   /r   15 ≦0.2  (15) 
 
     where,
 r 15 : radius of curvature of the object side surface of the lens element of the third lens element group. 
 
   
   
     7. A camera which installs thereon the zoom lens according to  claim 6 . 
   
   
     8. A camera which installs thereon the zoom lens according to  claim 1 .